1. Field of the Invention
The present invention relates to biomimetic electro-active paper actuators, which are ultra light, have a large deformation feature, are operated with low power consumption, are remotely driven by microwaves and have suitable response speed, and also relates to a method thereof.
2. Description of the Prior Art
Industrial interest in electro-active polymers (EAP) has increased because of the possibility of artificial muscles as functional materials capable of deforming largely. EAP has flexibility like a muscle as well as it can be deformed largely by outer stimulation, and has features and functions that other materials do not. EAP creates applications of artificial muscle actuators such as for next generation robots, applications in the entertainment industry or the actuators of a micro air plane. The application of EAP actuators is broad, and provides utility to many industry fields. However, since the EAPs developed until now have limited function, new EAP materials development is essential. There are many problems with EAP that need to be solved, including operation force increase, more rapid response, lower power consumption, and improved durability etc. Particularly, in ultra light EAP actuators, power supplying is very important when it is associated with the application device.
Generally EAP is classified according to operating principle as either electronic EAP or ionic EAP:                1. Electronic EAP: Dr. Zhang of Pennsylvania University has obtained remarkable piezoelectric phenomenon from an electronic radiated P (VDF-TrFE) copolymer. When 150 V/μm is applied at low frequency into the copolymer, about 4% piezoelectric deformation rate can be obtained and it has an elasticity constant of more than 1 GPa. However, disadvantages are high production cost because of the irradiation usage and the need for a high actuation voltage. This is used in acoustic transducer development to be used in medical probing apparatus, underwater acoustic devices, stereo speakers and the like. SRI International has developed EAP actuators based on electrostictive response of dielectric elastomers covered with a flexible electrode in the presence of an electric field. Double bow-tie or roll typed linear actuators using acryl film were utilized in the artificial muscle of biomimetic robots such as a 6-axials walking robot, a flapping wing of a micro air plane and the like. However, there are disadvantages that high voltage of about 200 V/μm must be applied and pre-strain must be given in lengthwise. NASA Langley research center has developed a piezoelectric polymer of grafted elastic copolymer that has a deformation rate of about 4% and a high physical elasticity constant of 560 MPa at 140 V/μm. The grafted elastic copolymer comprises grafted polymer composing crystal in backbone having flexibility. A problem these electronic EAPs have is that they need a high operating voltage, resulting in that there are many difficulties in voltage breakdown, packaging, miniaturization, device design and implementation.        2. Ionic EAP: An ionic polymer gel is capable of being fabricated into actuators exhibiting force and energy density similar to human muscles. Calvert of Arizona University made an actuator capable of operating like muscle by stacking cross-linked poly acryl amide and polyacrilic acid hydrogel alternately between electrodes. It is bent according to electric field when hydrogel is placed on water between two electrodes. However, since this multilayer ionic gel structure needs time for the ion to be diffused into the gel, the response is slow. Ionomeric polymer-metal composites (IPMC) are ionic EAP where the polymer net is bent by cation migration at the electric field applied. Many researchers including Oguro of Advanced Institute of Science and Technology in Japan, Shahinpoor of New Mexico University etc. have investigated the operating principle and functions of IPMC. By using IPMCs, demonstrations have been made such as a dust wiper, a gripper, a non-noise swimming robot, an active catheter, a cilium-like assembled robot, an artificial tactile system similar to coral reef, and the like. Conducting polymer (CP) is operated by reversible counter-ion charge and discharge generated during the redox cycle. Actuators using CP have been developed in many countries including USA, Japan, Australia, Italy, Spain etc, and bilayer structures and trilayer structures have been developed with a stack of CP films and an elastic film without volume deformation. Sweden Linkopings University has successfully made a robot arm having an elbow, wrist and 2-4 fingers able to be separately controlled by using a conducting polymer actuator, and to move a 0.1 mm glass ball about 0.25 mm distance. The actuator using single-walled carbon nanotubes generates more strain than that of natural muscle and higher deformation than ferroelectrics having a high elasticity constant. Macro SWNT actuator such as natural muscle is a type wherein several billion nanotubes are combined, and long durability can be achieved because of not needing ion exchange which reduces lifetime, and because it is operated at low voltage. These ionic EAPs have disadvantages that operating speed is slow and there must be an electrolyte and water present while having the advantage that the operating voltage is low.        
As described above, electronic EAPs developed until now have rapid response and large deformation rate but need a high operating voltage, while ionic EAPs can be deformed at low operating voltage and have elasticity like muscle but response speed is low and wetness should be kept.
On the other hand, in applications needing ultra light and large deformation features such as micro crawling robots, micro air planes, and animatronic devices, the above-mentioned requirements are essential. For applications needing ultra light and large deformation features, EAP needs rapid response, low power consumption, and good durability. Particularly, since an ultra lightweight EAP application device cannot carry power batteries, it is desirable to use a remote power source for reducing the weight as well as minimizing the power consumption. If a remote power source is used, EAP applications can be broadened due to the device being lighter, lower power consumption and improved performance.